Swage baseplates are commonly used in disk drive or other dynamic data storage systems to attach head suspensions to actuator arms. Examples of these attachment structures and associated assembly methods for magnetic disk drives are disclosed in U.S. Pat. No. 6,697,224 (Wang), U.S. Pat. No. 6,033,755 (Hanrahan) and U.S. Pat. No. 6,183,841 (Hanrahan), all of which are incorporated herein by reference.
Briefly, baseplates include a generally flat flange and a tubular boss tower extending from the flange. The boss tower is hollow and has an inner diameter defining a swaging opening and an outer diameter sized to fit within an opening in the actuator arm to which the suspension is to be mounted. The flange also has an opening generally concentric with the swaging opening and defined by a secondary inner or back bore diameter. The boss tower inner diameter is typically smaller than the back bore diameter. A shoulder area defines a transition from the larger flange opening to the smaller swaging opening.
The flange is typically welded to a mounting region of the suspension. An actuator arm having an opening therethrough is positioned over the boss tower so that the actuator opening and the boss tower are concentrically aligned. During the swaging process a ball is forced from the flange opening through the swaging opening in the boss tower, bending the boss tower outwardly at the shoulder area, thereby forcing the outer surface of the boss tower into frictional engagement with an inner surface of the opening in the actuator arm. This is known as torque retention. The baseplate and attached suspension are thereby securely fastened to the actuator arm. Unfortunately, this swaging process can result in deformation of the baseplate flange section, and in turn the suspension to which the baseplate is mounted. This deformation can cause changes in the desired positional orientation of the suspension, known as z-height variations, and changes to the desired spring characteristics of the suspension, know as gram changes. These swaging-induced z-height variations and gram changes can detrimentally affect the operational performance of the suspension.
Attempts have been made in the past to address the above described problems associated with swaging-induced z-height variations and gram changes. U.S. Pat. No. 6,424,497 (Coon) teaches that where the inner diameter of the bore (boss tower) is about 95-99% of the diameter of the flange opening, swaging induced deformations are reduced.
Swaging baseplates generally protrude somewhat from the mounted actuator arm. Swaging baseplates that have a low-profile, or that protrude minimally from the actuator arm, are desirable as they have less mass and take up less space in the suspension assembly, permitting smaller assemblies or allowing more room for other components. However, reduction in baseplate profile generally reduces the torque retention provided by the swaged baseplate. The strength of the coupling between the actuator arm and the suspension assembly is thereby undesirably weakened.
Attempts have been made to design a low profile baseplate capable of maintaining adequate torque retention. U.S. Pat. No. 5,689,389 (Braunheim) teaches that the swage mount vertical profile may be reduced by a factor of three while still maintaining adequate torque retention where the inner diameter of the hub (boss tower) is at least 85% of the baseplate opening diameter, but no greater than the baseplate opening diameter. U.S. Pat. No. 6,183,841 (Hanrahan, et. al.) teaches that a low profile swage mount is achievable where:Wh/Tbp*Wh/((His+Hh−Hcb)/2)≧5
Wh is the hub radial width, Tbp is the base plate thickness, His is the hub inner surface depth, Hh is the overall height and Hcb is the counter bore depth.
However, a need still exists for a swaging assembly that withstands transfer of deformation from the boss tower to the baseplate flange area. The baseplate must also be capable of maintaining sufficient torque retention while displaying a low vertical profile.